Pilot signal transmission for an orthogonal frequency division wireless communication system

ABSTRACT

Transmission patterns for pilot symbols transmitted from a mobile station or base station are provided. The pattern allows for improved receipt of the pilot symbols transmitted. In addition, schemes for improving the ability to multiplex pilot symbols without interference and/or biasing from different mobile stations over the same frequencies and in the same time slots.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

The present Application for Patent is related to the followingco-pending U.S. Patent Application:

“PILOT SIGNAL TRANSMISSION FOR AN ORTHOGONAL FREQUENCY DIVISION WIRELESSCOMMUNICATION SYSTEM” patent application Ser. No. 11/083,693, filed Mar.17, 2005, assigned to the assignee hereof, and expressly incorporated byreference herein.

BACKGROUND

I. Field

The present document relates generally to wireless communication andamongst other things pilot information transmission in an orthogonalfrequency division wireless communication system.

II. Background

An orthogonal frequency division multiple access (OFDMA) system utilizesorthogonal frequency division multiplexing (OFDM). OFDM is amulti-carrier modulation technique that partitions the overall systembandwidth into multiple (N) orthogonal frequency subcarriers. Thesesubcarriers may also be called tones, bins, and frequency channels. Eachsubcarrier may be modulated with data. Up to N modulation symbols may besent on the N total subcarriers in each OFDM symbol period. Thesemodulation symbols are converted to the time-domain with an N-pointinverse fast Fourier transform (IFFT) to generate a transformed symbolthat contains N time-domain chips or samples.

In a frequency hopping communication system, data is transmitted ondifferent frequency subcarriers in different time intervals, which maybe referred to as “hop periods.” These frequency subcarriers may beprovided by orthogonal frequency division multiplexing, othermulti-carrier modulation techniques, or some other constructs. Withfrequency hopping, the data transmission hops from subcarrier tosubcarrier in a pseudo-random manner. This hopping provides frequencydiversity and allows the data transmission to better withstanddeleterious path effects such as narrow-band interference, jamming,fading, and so on.

An OFDMA system can support multiple mobile stations simultaneously. Fora frequency hopping OFDMA system, a data transmission for a given mobilestation may be sent on a “traffic” channel that is associated with aspecific frequency hopping (FH) sequence. This FH sequence indicates thespecific subcarrier to use for the data transmission in each hop period.Multiple data transmissions for multiple mobile stations may be sentsimultaneously on multiple traffic channels that are associated withdifferent FH sequences. These FH sequences may be defined to beorthogonal to one another so that only one traffic channel, and thusonly one data transmission, uses each subcarrier in each hop period. Byusing orthogonal FH sequences, the multiple data transmissions generallydo not interfere with one another while enjoying the benefits offrequency diversity.

An accurate estimate of a wireless channel between a transmitter and areceiver is normally needed in order to recover data sent via thewireless channel. Channel estimation is typically performed by sending apilot from the transmitter and measuring the pilot at the receiver. Thepilot signal is made up of pilot symbols that are known a priori by boththe transmitter and receiver. The receiver can thus estimate the channelresponse based on the received symbols and the known symbols.

Part of each transmission from any particular mobile station to the basestation, often referred to as a “reverse link” transmission, during ahop period is allocated to transmitting pilot symbols. Generally, thenumber of pilot symbols determines the quality of channel estimation,and hence the packet error rate performance. However, the use of pilotsymbols causes a reduction in the effective transmission data rate thatcan be achieved. That is, as more bandwidth is assigned to pilotinformation, less bandwidth becomes available to data transmission.

One type of FH-OFDMA system is a blocked hop system where multiplemobile stations are assigned to a contiguous group of frequencies andsymbol periods. In such a system, it is important that pilot informationbe reliably received from the mobile station, while at the same timereducing the bandwidth that is allocated to pilot information, since theblock has a limited amount of symbols and tones available to be used forboth pilot and data transmission.

SUMMARY

In an embodiment, pilot symbol patterns are provided for pilot symbolstransmitted from a mobile station or a base station. The pattern allowsfor improved receipt and demodulation of the pilot symbols transmitted.

In additional embodiments, schemes for improving the ability tomultiplex pilot symbols without interference and/or biasing fromdifferent mobile stations in a same sector of a base station over thesame frequencies and in the same time slots in an OFDM system areprovided.

In further embodiments, schemes for reducing the bias or interferencefor pilot symbols transmitted from different mobile stations inneighboring cells over the same frequencies and in the same time slotsin an OFDM system are provided.

In other embodiments, methods for altering pilot symbol patterns areprovided. Also, in other further embodiments methods for generatingpilot symbols are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present embodiments maybecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 illustrates a multiple access wireless communication systemaccording to an embodiment;

FIG. 2 illustrates a spectrum allocation scheme for a multiple accesswireless communication system according to an embodiment;

FIG. 3A illustrates a block diagrams of a pilot assignment schemeaccording to an embodiment;

FIG. 3BA illustrates a block diagrams of a pilot assignment schemeaccording to another embodiment;

FIG. 4A illustrates a pilot symbol scrambling scheme according to anembodiment;

FIG. 4B illustrates a pilot symbol scrambling scheme according toanother embodiment;

FIG. 5 illustrates a base station with multiple sectors in a multipleaccess wireless communication system according to an embodiment;

FIG. 6 illustrates a multiple access wireless communication systemaccording to another embodiment;

FIG. 7 illustrates a block diagram of an embodiment of a transmittersystem and a receiver system in a multi-input multi-output multipleaccess wireless communication system;

FIG. 8 illustrates a flow chart of a method of pilot symbol generationaccording to an embodiment; and

FIG. 9 illustrates a flow chart of a method of altering pilot symbolpatterns according to an embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a multiple access wireless communication systemaccording to an embodiment is illustrated. A base station 100 includesmultiple antenna groups 102, 104, and 106 each including one or moreantennas. In FIG. 1, only antenna is shown for each antenna group 102,104, and 106, however, multiple antennas may be utilized for eachantenna group that corresponds to a sector of base station 100. Mobilestation 108 is in communication with antenna 104, where antenna 104transmits information to mobile station 108 over forward link 114 andreceives information from mobile station 108 over reverse link 112.Mobile station 110 is in communication with antenna 106, where antenna106 transmits information to mobile station 110 over forward link 118and receives information from mobile station 110 over reverse link 116.

Each group of antennas 102, 104, and 106 and/or the area in which theyare designed to communicate is often referred to as a sector of the basestation. In the embodiment, antenna groups 102, 104, and 106 each aredesigned to communicate to mobile stations in a sector, sectors 120,122, and 124, respectively, of the areas covered by base station 100.

A base station may be a fixed station used for communicating with theterminals and may also be referred to as an access point, a Node B, orsome other terminology. A mobile station may also be called a mobilestation, a user equipment (UE), a wireless communication device,terminal, access terminal or some other terminology.

Referring to FIG. 2, a spectrum allocation scheme for a multiple accesswireless communication system is illustrated. A plurality of OFDMsymbols 200 is allocated over T symbol periods and S frequencysubcarriers. Each OFDM symbol 200 comprises one symbol period of the Tsymbol periods and a tone or frequency subcarrier of the S subcarriers.

In an OFDM frequency hopping system, one or more symbols 200 may beassigned to a given mobile station. In an embodiment of an allocationscheme as shown in FIG. 2, one or more hop regions, e.g. hop region 202,may be comprised of symbols assigned to a group of mobile stations forcommunication over a reverse link. Within each hop region, assignment ofsymbols may be randomized to reduce potential interference and providefrequency diversity against deleterious path effects.

Each hop region 202 includes symbols 204 that are assigned to the one ormore mobile stations that are in communication with the sector of thebase station and assigned to the hop region. In other embodiments, eachhop region is assigned to one or more mobile stations. During each hopperiod, or frame, the location of hop region 202 within the T symbolperiods and S subcarriers varies according to a hopping sequence. Inaddition, the assignment of symbols 204 for the individual mobilestations within hop region 202 may vary for each hop period.

The hop sequence may pseudo-randomly, randomly, or according to apredetermined sequence, select the location of the hop region 202 foreach hop period. The hop sequences for different sectors of the samebase station are designed to be orthogonal to one another to avoid“intra-cell” interference among the mobile station communicating withthe same base station. Further, hop sequences for each base station maybe pseudo-random with respect to the hop sequences for nearby basestations. This may help randomize “inter-cell” interference among themobile stations in communication with different base stations.

In the case of a reverse link communication, some of the symbols 204 ofa hop region 202 are assigned to pilot symbols that are transmitted fromthe mobile stations to the base station. The assignment of pilot symbolsto the symbols 204 should preferably support space division multipleaccess (SDMA), where signals of different mobile stations overlapping onthe same hop region can be separated due to multiple receive antennas ata sector or base station, provided enough difference of spatialsignatures corresponding to different mobile stations. To moreaccurately extract and demodulate signals of different mobile stations,the respective reverse link channels should be accurately estimated.Therefore, it may be desired that pilot symbols on the reverse linkenable separating pilot signatures of different mobile stations at eachreceive antenna within the sector in order to subsequently applymulti-antenna processing to the pilot symbols received from differentmobile stations.

Block hopping may be utilized for both the forward link and the reverselink, or just for the reverse link depending on the system. It should benoted that while FIG. 2 depicts hop region 200 having a length of sevensymbol periods, the length of hop region 200 can be any desired amount,may vary in size between hop periods, or between different hoppingregions in a given hop period.

It should be noted that while the embodiment of FIG. 2 is described withrespect to utilizing block hopping, the location of the block need notbe altered between consecutive hop periods or at all.

Referring to FIGS. 3A and 3B, block diagrams of pilot assignment schemesaccording to several embodiments are illustrated. Hop regions 300 and320 are defined by T symbol periods by S subcarriers or tones. Hopregion 300 includes pilot symbols 302 and hop region 320 includes pilotsymbols 322, with the remaining symbols periods and tone combinationsavailable for data symbols and other symbols. In an embodiment, pilotsymbol locations for each hop regions, i.e. a group of N_(S) contiguoustones over N_(T) consecutive OFDM symbols, should have pilot toneslocated close to the edges of the hop region. This is generally becausetypical channels in wireless applications are relatively slow functionsof time and frequency so that a first order approximation of thechannel, e.g. a first order Taylor expansion, across the hop region intime and frequency provides information regarding channel conditionsthat is sufficient to estimate the channel for a given mobile station.As such, it is preferred to estimate a pair of channel parameters forproper receipt and demodulation of symbols from the mobile stations,namely the constant component of the channel, a zero order term of aTaylor expansion, and the linear component, a first order term Taylorexpansion, of the channel across the time and frequency span of thechannel. Generally estimation accuracy of the constant component isindependent of pilot placement. The estimation accuracy of the linearcomponent is generally preferably achieved with pilot tones located atthe edges of the hop region.

Pilot symbols 302 and 322 are arranged in contiguous pilot symbolclusters 304, 306, 308, and 310 (FIG. 3A) and 324, 326, 328, and 330(FIG. 3B). In an embodiment, each cluster 304, 306, 308, and 310 (FIG.3A) and 324, 326, 328, and 330 (FIG. 3B) within a hop region, has afixed number, and often the same number, of pilot symbols within a givenhop region. The utilization of clusters 304, 306, 308, and 310 (FIG. 3A)and 324, 326, 328, and 330 (FIG. 3B) of contiguous pilot symbols may, inan embodiment take into account the effect of a multi-user interferencecaused by inter-carrier interference which results from high Dopplerand/or symbol delay spreads. Further, if pilot symbols from mobilestations scheduled on a same hop region are received at substantiallydifferent power levels, signals of a stronger mobile station may createa significant amount of interference for a weaker mobile station. Theamount of interference is higher at the edges, e.g. subcarrier 1 andsubcarrier S, of the hop region and also at the edge OFDM symbols, e.g.symbol periods 1 and T, when the leakage is caused by excess delayspread, i.e. when the portion of channel energy concentrated in the tapsthat exceed cyclic prefix of the OFDM symbols becomes significant.Therefore, if pilot symbols are located exclusively at the edges of ahop region there may be degradation in channel estimation accuracy and abias in interference estimation. Hence, as depicted in FIGS. 3A and 3Bpilot symbols are placed close to the edges of the hop region, however,avoiding the situation where all the pilot symbols are at the edges ofthe hop region.

Referring to FIG. 3A, a hop region 300 is comprised of pilot symbols302. In the case of channels with a pronounced frequency selectivityrather than time selectivity, pilot symbols 302 are located incontiguous pilot symbol clusters 304, 306, 308, and 310 with each pilotsymbol cluster 304, 306, 308, and 310 spanning multiple symbol periodsand one frequency tone. The frequency tone is preferably chosen to beclose to the edges of the frequency range of the hop region 300,however, not exactly at the edge. In the embodiment of FIG. 3A, none ofthe pilot symbols 302 in a given cluster are at the edge frequency tonesand in each cluster only one pilot symbol may be at an edge symbolperiod.

One rationale behind a “horizontal” shape of the contiguous pilot symbolclusters of pilot symbols 302 is that, for channels with higherfrequency selectivity, the first order (linear) component may bestronger in the frequency domain than in the time domain.

It should be noted that one or more pilot symbols in each cluster, inthe embodiment of FIG. 3A, may be at a different tone than one or morepilot symbols in a different cluster. For example, cluster 304 may be attone S and cluster 306 may be at tone S-1.

Referring to FIG. 3B, in the case of channels with a pronounced timeselectivity rather than frequency selectivity, pilot symbols 322 arearranged in clusters 324, 326, 328, and 330 of contiguous pilot symbolsthat each span multiple frequency tones but have a same symbol period ofhop region 320. OFDM symbols at the edges of hop region 320, those thathave a maximum tone, e.g. tone S, or minimum tone, e.g. tone 1, of thefrequency range that defines the S subcarriers, may be included as partof the pilot symbols, since there may be pilot symbols 322 that are atthe edges of the hop region 320. However, in the embodiment shown inFIG. 3B, only one pilot symbol in each cluster may be assigned to themaximum or minimum frequency subcarrier.

In the embodiment depicted in FIG. 3B, a channel with higher timeselectivity may have a typical pattern that may be obtained by a 90°rotation of the pattern chosen for channels with higher frequencyselectivity (FIG. 3A).

It should be noted that one or more pilot symbols in each cluster, inthe embodiment of FIG. 3B, may be assigned to a different symbol periodthan one or more pilot symbols in a different cluster. For example,cluster 324 may be at different symbol period T than cluster 326.

Additionally, as depicted in the embodiments of FIGS. 3A and 3B, pilotpatterns are provided so that the clusters, 304, 306, 308, and 310 (FIG.3A) and 324, 326, 328, and 330 (FIG. 3B), are preferably symmetric withrespect to the center of the hop region. The symmetry of the clusterswith respect to the center of the hop region may provide improvedsimultaneous estimation of the channel with respect to time andfrequency responses of the channel.

It should be noted that while FIGS. 3A and 3B depict four clusters ofpilot symbols per hop region, a fewer or greater amount of clusters maybe utilized in each hop region. Further, the number of pilot symbols perpilot symbol cluster may also vary. The total number of pilot symbolsand pilot symbol clusters are a function of the number of pilot symbolsrequired by the base station to successfully demodulate data symbolsreceived on the reverse link and to estimate the channel between thebase station and the mobile station. Also, each cluster need not havethe same number of pilot symbols. The number of mobile stations that canbe multiplexed over a single hop region can, in an embodiment, be equalto the number of pilot symbols in a hop region.

In addition, while FIGS. 3A and 3B depict pilot symbol clusters designedeither for channels having frequency selectivity or time selectivity thepilot pattern may be such that there are clusters for frequencyselective channels as well as clusters for time selective channels inthe same pilot pattern, e.g. some clusters arranged in the pattern ofclusters 304, 306, 308, or 310 and some clusters arranged in the patternof clusters 324, 326, 328, or 330.

In some embodiments, the pilot pattern chosen to be utilized may bebased upon the conditions for which the channel is being optimized. Forexample, for channels that may have high-speed movement, e.g. vehicular,of mobile stations a time-selective pilot pattern may be preferred,whereas for slow-speed movement of mobile station, e.g. pedestrians, afrequency selective pilot pattern may be utilized. In other embodiment,the pilot pattern can be chosen based upon channel conditions, adetermination made after a pre-determined number of hop periods.

Referring to FIGS. 4A and 4B, pilot allocation schemes according tofurther embodiments are illustrated. In FIG. 4A, hop regions 400includes pilot symbols C_(1,q), C_(2,q), and C_(3,q), arranged incluster 402; C_(4,q), C_(5,q), and C_(6,q), arranged in cluster 404;C_(7,q), C_(8,q), and C_(9,q), arranged in cluster 406; and C_(10,q),C_(11,q), and C_(12,q) arranged in cluster 408. In an embodiment, inorder to improve spatial diversity in hop regions where multiple mobilestations provide overlapping pilot symbols, the pilot symbols ofdifferent mobile stations should be multiplexed in such a way over thesame OFDM symbol period and tone so that the pilot symbols aresubstantially orthogonal when received at the antennas of the cluster ofthe base station.

In FIG. 4A, each of the pilot symbols C_(1,q), C_(2,q), C_(3,q),C_(4,q), C_(5,q), C_(6,q), C_(7,q), C_(8,q), C_(9,q), C_(10,q),C_(11,q), and C_(12,q) are assigned to multiple mobile stations of hopregion 400, that is each symbol period includes multiple pilot symbols,from a number of different mobile station stations. Each of the pilotsymbols in a pilot symbol cluster, e.g. cluster 402, 404, 406, and 408,are generated and transmitted in such a way that a receiver of thepilots symbols in the cluster, e.g. base station, can receive them sothat they are orthogonal with respect to the pilot symbols from eachother mobile station in the same cluster. This can be done by applying apredetermined phase shift, e.g. a scalar function to multiply, each ofthe samples constituting the pilot symbols transmitted by each of themobile stations. To provide orthogonality, the inner products of vectorsrepresenting the sequence of the scalar functions in each cluster foreach mobile station may be zero.

Further, in some embodiments, it is preferred that the pilot symbols ofeach cluster are orthogonal to the pilot symbols of each other clusterof the hop region. This can be provided in the same manner asorthogonality is provided for the pilot symbols within each cluster froma different mobile station, by utilizing a different sequence of scalarfunctions for the pilot symbols of each mobile station in each clusterof pilot symbols. Mathematical determination of orthogonality can bemade by selecting a sequence of scalar multiples for each of the pilotsymbols for a particular cluster for the particular mobile station thevector of which is orthogonal, e.g. the inner product is zero, withrespect to a vector representing the sequence of scalar multiples usedfor the pilot symbols of the other mobile stations in all the clustersand the same mobile station in the other clusters.

In an embodiment the number of mobile stations that may be supported,where orthogonality of the pilot symbols across each of the clusters isprovided, is equal to the number of pilot symbols that are provided perpilot symbol cluster.

In the embodiments of FIGS. 4A and 4B, the q-th user of Q overlappingusers, 1≦q≦Q, uses the sequence S of size N_(P), where N_(P) is thetotal number of pilot tones (In FIGS. 4A and 4B, N_(P)=12):S_(q)=[S_(1,q) . . . S_(N) _(P) _(,q)]^(T), 1≦q≦Q,  (1)here (^(T)) denotes transpose of the matrix containing the sequences. Asdiscussed above, the sequences of scalar functions, in each cluster ofpilot symbols, should be different for different mobile stations inorder to obtain consistent estimates of the respective channels throughthe reduction of interference between pilot symbols. Moreover, thesequences should be linearly independent, as such it is preferred thatno sequence or vector be a linear combination of the remainingsequences. Mathematically, this may defined in that the N_(P)×Q matrixS=[S₁ . . . S_(Q)]  (2)is of full column rank. It should be noted in the expression (2) abovematrix Q≦N_(P). That is, the number of overlapping mobile stationsshould not exceed the number of total pilot symbols in the hop region.

Based upon the above, any set of sequences Q with a full-rank S enablesconsistent channel estimation. However, in other embodiment, the actualestimation accuracy may depend on the correlation properties of S. In anembodiment, as can be determined utilizing equation (1), performance maybe improved when any two sequences are mutually (quasi-) orthogonal inthe presence of the channel. Mathematically, this condition may bedefined by

$\begin{matrix}{{{\sum\limits_{k = 1}^{N_{P}}{H_{k}S_{k,p}^{*}S_{k,q}}} \approx {0\mspace{31mu}{for}\mspace{14mu}{all}\mspace{14mu} 1} \leq p},{q \leq Q},} & (3)\end{matrix}$where H_(k) is a complex channel gain corresponding to the k-th pilotsymbol, 1≦k≦N_(P). In a time and frequency invariant channel H₁=H₂=. . .=H_(N) _(P) ) condition (3) reduces to the requirement of mutuallyorthogonal sequences:

$\begin{matrix}{{{\sum\limits_{k = 1}^{N_{P}}{S_{k,p}^{*}S_{k,q}}} \approx {0\mspace{31mu}{for}\mspace{14mu}{all}\mspace{14mu} 1} \leq p},{q \leq Q},} & (4)\end{matrix}$enforcing this condition for any possible channel realization from atypical set of channels may be impractical. In fact, expression (3) maybe satisfied when a channel exhibits limited time and frequencyselectivity, which is the case of pedestrian channels with a relativelysmall delay spread. However, the conditions may be substantiallydifferent on vehicular channels and/or channels with a significant delayspread, thereby resulting in performance degradation.

As discussed with respect to FIGS. 3A and 3B, pilot allocation patternsconsist of a few clusters of pilot symbols placed close to the edges ofthe hop region, where each cluster is contiguous in time (FIG. 3A)and/or frequency (FIG. 3B). Since channel variations inside everycluster are generally limited, due to contiguous nature of the pilotsymbols in time and frequency and continuity of the channel in time andfrequency. Hence making different sequences orthogonal over each clusterallows condition (3) to be met. A potential drawback of this solution isthat the number of overlapping mobile stations that can be orthogonalover every cluster is limited to the size of the cluster, denoted hereN_(C). In the example shown in FIGS. 4A and 4B, N_(C)=3, and hence up toQ=3 mobile stations can be separated orthogonally in such an embodiment.In fact, a fairly small number of Q is sufficient in many practicalscenario. When Q>N_(C), it may be difficult to keep all mobile stationsorthogonal over every cluster, since there may be some inter-symbolinterference. Hence, approximate orthogonality may be sufficient, withsome performance loss of time and/or frequency varying channels ifQ>N_(C).

In an embodiment, a set of design parameters for the sequences of scalarfunctions S=[S₁ . . . S_(Q)] may be defined by:

-   -   Any two sequences are orthogonal over the entire set of pilot        symbols, thereby satisfying

$\begin{matrix}{{{\sum\limits_{k = 1}^{N_{P}}{S_{k,p}^{*}S_{k,q}}} = {{0\mspace{31mu}{for}\mspace{14mu}{all}\mspace{14mu} 1} \leq p}},{q \leq Q},} & (5)\end{matrix}$

-   -   Subsequent groups of N_(C) sequences are such that any two        sequences within a group are mutually orthogonal over any        cluster of pilots:

$\begin{matrix}{{{\sum\limits_{k = 1}^{N_{C}}{S_{{k + {IN}_{C}},p}^{*}S_{{k + {IN}_{C}},q}}} = 0},{{{nN}_{C} + 1} \leq p},{q \leq {\min\left\{ {{\left( {n + 1} \right)N_{C}},Q} \right\}}},{0 \leq n < \frac{Q}{N_{C}}},{0 \leq l < {M_{C}.}}} & (6)\end{matrix}$

-   -   All the elements S_(k,q) of all the sequences have substantially        equal absolute values, e.g. approximately the same power.        where M_(C) denotes the total number of clusters of size N_(C),        so that the number of pilots N_(P)=M_(C)N_(C).

In an embodiment, the sequences S=[S₁ . . . S_(Q)] are created usingexponential functions so that so that the same energy per symbolprovided by each sequence. Further, in this embodiment, the groups ofN_(C) sequences may be made mutually orthogonal within each cluster,regardless of cluster size since exponents are not limited to particularmultiples, and with the sequences used in every other cluster across allof the pilot symbols, by (i) defining exponential sequences within eachcluster; and (ii) populating the intra-cluster portions across clusters.This can be seen equation (7) where a N×N Discrete Fourier Transform(DFT) basis is defined.

$\begin{matrix}{{F(N)} = {\begin{bmatrix}{F_{1,1}(N)} & {F_{1,2}(N)} & \cdots & {F_{1,N}(N)} \\{F_{2,1}(N)} & {F_{2,1}(N)} & \ddots & {F_{2,N}(N)} \\\vdots & \vdots & \ddots & \vdots \\{F_{N,1}(N)} & {F_{N,2}(N)} & \cdots & {F_{N,N}(N)}\end{bmatrix} = {\quad\begin{bmatrix}1 & 1 & \cdots & 1 \\{\mathbb{e}}^{{t2\pi}\frac{1}{N}} & {\mathbb{e}}^{{t2\pi}\frac{2}{N}} & \ddots & {\mathbb{e}}^{t\; 2\pi\frac{{({N - 1})}2}{N}} \\\vdots & \vdots & \ddots & \vdots \\{\mathbb{e}}^{{t2\pi}\frac{N - 1}{N}} & {\mathbb{e}}^{{t2\pi}\frac{2{({N - 1})}}{N}} & \cdots & {\mathbb{e}}^{{t2\pi}\frac{{({N - 1})}{({N - 1})}}{N}}\end{bmatrix}}}} & (7)\end{matrix}$

The above expression (7) may be written in a compact block form asfollows:S=[S ₁ . . . , S _(Q) ]=

F(M _(C))

F(N_(C))

_(:,1:Q)  (8)where

•

_(:,1:Q) denotes matrix block spanned by columns 1 through Q of theoriginal matrix. A more general form of S may be given byS=[S₁, . . . , S_(Q)]=

V

_(:,1:Q)  (9)where U is an arbitrary N_(C)×N_(C) unitary matrix (U*U=I_(N) _(P) ) andV is an arbitrary M_(C)×M_(C) unitary matrix (U*U=I_(M) _(C) ).

In an embodiment the number of mobile stations that may be supported,where orthogonality of the pilot symbols across each of the clusters isprovided, is equal to the number of pilot symbols that are provided perpilot symbol cluster.

In an embodiment, the exponential functions utilized to multiply thesamples of the pilot symbols are generated utilizing a discrete Fouriertransform function, which is well known. In embodiments where thediscrete Fourier transform function is used to generate the symbols fortransmission, an extra phase shift is applied during formation of thesymbols using the discrete Fourier transform function in generating thesymbols for transmission.

In the embodiments of FIGS. 4A and 4B, the inner products of vectorsrepresenting the sequence of the scalar functions in each cluster foreach mobile station may be zero. However, in other embodiments this isnot the case. It may be arranged so that only quasi-orthogonalitybetween the sequences of the scalar functions in each cluster for eachmobile station is provided.

Further in those situations, where the number of mobile stationsassigned to the hop region is less than the number of pilot symbolsassigned to the hop region, the scalar shifts may still be decoded atthe base station in order to be utilized to perform interferenceestimation. Therefore, these pilot symbols may be utilized forinterference estimation since they are orthogonal or quasi-orthogonalwith respect to pilot symbols by the other mobile stations assigned tothe hop region.

Referring to FIG. 5, a base station with multiple sectors in a multipleaccess wireless communication system according to an embodiment isillustrated. A base station 500 includes multiple antenna groups ofantennas 502, 504, and 506. In FIG. 5, only one antenna is shown foreach antenna group 502, 504, and 506, however, multiple antennas may beutilized. The multiple antennas of each antenna group 502, 504, and 506may be utilized to provide spatial diversity at the base station tosignals transmitted from mobile stations in a corresponding sector, inaddition to the spatial diversity provided to the different physicallocations of the different mobile stations.

Each antenna group 502, 504, and 506 of base station 500 is configuredto communicate with mobile stations in a sector to be covered by basestation 500. In the embodiment of FIG. 5, antenna group 502 coverssector 514, antenna group 504 covers sector 516, and antenna group 506covers sector 518. Within each sector, as described with respect to FIG.4, the pilot symbols transmitted from the mobile stations may beaccurately demodulated and used for channel estimation, and otherfunctionally, at the base station due the orthogonality or theapproximately orthogonality between all of the inter-sector pilot symbolclusters.

However, intra-sector interference may exist for mobile stations nearthe boundary of a sector, e.g. mobile station 510 which is near aboundary of sectors 514 and 516. In such a case, pilot symbols frommobile station 510 may be at lower powers than pilot symbols from othermobile stations in both sectors 514 and 516. In such a situation, mobilestation 510 could eventually benefit from reception at both sectorsantennas, especially when its channel to the serving sector, i.e. sector516 signals may fade if power is increased from antenna 504. In order tofully benefit from the reception from antenna 502 of sector 514,accurate estimate of the channel of mobile station 510 between antenna502 of sector 514 should be provided. However, if the same orsubstantially the same sequences are used for the scalar multiples ofthe pilot symbols in different sectors with the present pilot design,pilot symbols transmitted by mobile station 510 may collide with pilotsymbols transmitted by mobile station 508 which is scheduled in sector514 on the same hop region as mobile station 510 is scheduled in sector516. Further, in some cases depending on the power control strategyutilized by the base station to control the mobile stations, the powerlevel of symbols from mobile station 508 may substantially exceed thesignal level of mobile station 510 at antenna group 502 of the sector514, especially when mobile station 508 is close to the base station500.

In order to combat the intra-sector interference that may arise,scrambling codes may be used for the mobile stations. The scramblingcode may be unique to individual mobile stations or may be the same foreach of the mobile stations communicating with an individual sector. Inan embodiment, these specific scrambling codes allow antenna group 502to see a composite channel of mobile stations 508 and 510.

In the case where a single mobile station is assigned to an entire hopregion, user specific scrambling sequences may be provided so that everymobile station in a given sector makes use of the same pilot sequence;the construction of these sequences is described with respect to FIGS.4A and 4B. In the example of FIG. 5, mobile stations 508, 510, and 512may have different user specific scrambling sequences and thereforesufficient channel estimation may be achieved.

Where multiple mobile stations are, or may be, assigned to a same hopregion, two approaches may be utilized to reduce intra-clusterinterference. Firstly, user specific scrambling sequences may beutilized if the cluster size N_(C) is greater or equal than the numberof overlapping mobile stations in each sector Q times the number ofsectors in the cell. If this is the case, distinct sets of Q differentuser-specific scrambling codes may be assigned to different sectors.

However, if the cluster size N_(C) is less than the number ofoverlapping mobile stations in each sector Q times the number of sectorsin the cell, this may be important if a goal of system design is to keepN_(C) to maintain a limited pilot overhead, user specific scramblingcodes may not be effective to reduce inter-cell interference. In suchcases, a sector specific scrambling sequence may be utilized along withthe user specific scrambling sequence.

A sector specific scrambling sequence is a sequence X_(S)=[X_(1,S), . .. , X_(N) _(P) _(,S)]^(T) of N_(P) complex functions that multiply therespective elements of the sequences S=[S₁ . . . S_(Q)], for all mobilestations in a same sector. In a cell consisting of S sectors, a set of Ssector specific scrambling sequences X₁, . . . , X_(S) may be utilizedto multiply the sequences S=[S₁ . . . S_(Q)] of the mobile stations. Insuch a case, mobile stations within different sectors, for examplesector 514 and 516 that may have mobile stations that utilize the sameuser specific scrambling sequences S=[S₁ . . . S_(Q)] may differ due todifferent sector specific scrambling sequences X_(S) ₁ and X_(S) ₂utilized to multiply the user specific scrambling sequence.

Similarly to user-specific scrambling, it is preferred that all of theentries of X₁, . . . , X_(S) have approximately equal absolute values tomaintain approximately equal power between the pilot symbols. In otherembodiments, it is preferred that entries of X₁, . . . , X_(S) be suchthat any pair of pilot symbols in a pilot symbol cluster, correspondingto any two combinations of user specific and sector specific scramblingsequences satisfies, should satisfy condition (3). One way to approachto the choice of contents of each sector specific sequence X₁, . . . ,X_(S) consists of an exhaustive search of sequences such as the elementsof every sequence are taken from some constant modulus (PSK)constellation such as QPSK, 8-PSK. The selection criterion may be basedupon the “worst case” channel estimation error variance corresponding tothe “worst” combination of mobile stations from different sectors anddifferent user specific scrambling that are based upon the potentialchannel environment. Channel estimation error may be computedanalytically based on statistical properties of the channel.Specifically, a trace of the covariance matrix of a channel estimatethat assume channel correlation structure based on an anticipated fadingmodel and parameters such as mobile station velocity, which defines timeselectivity, and propagation delay spread which defines frequencyselectivity. The analytical expressions for the minimum achievablechannel estimation error subject to a given correlation structure of thetrue channel are known in the art. Other similar criteria may be used tooptimize the choice of X₁, . . . , X_(S) as well.

In an embodiment where Quadrature Amplitude Modulation is utilized asthe modulation scheme, a set of sector specific scrambling sequences X₁,. . . , X_(S) that may be utilized is shown in Table 1 below. Each entryof the table specifies I and Q components of every X_(k,s), 1≦s≦S and1≦k≦N_(P) with S=3 and N_(P)=12.

TABLE 1 k 1 2 3 4 5 6 7 8 9 10 11 12 s = 1 {+1, +0} {+1, +0} {+1, +0}{+1, +0} {+1, +0} {+1, +0} {+1, +0} {+1, +0} {+1, +0} {+1, +0} {+1, +0}{+1, +0} s = 2 {+1, +0} {+1, +0} {−1, +0} {+1, +0} {+0, −1} {+1, +0}{+1, +0} {+0, −1} {+0, +1} {+0, +1} {+0, +1} {+0, +1} s = 3 {+0, +1}{−1, +0} {+1, +0} {+1, +0} {+0, +1} {+0, −1} {+0, −1} {+0, +1} {+1, +0}{+0, −1} {+1, +0} {−1, +0}

In an embodiment where Quadrature Amplitude Modulation is utilized asthe modulation scheme, a set of sector specific scrambling sequences X₁,. . . , X_(S) that may be utilized is shown in Table 1 below. Each entryof the table specifies I and Q components of every X_(k,s), 1≦s≦S and1≦k≦N_(P) with S=3 and N_(P)=12.

In some embodiments, each cell in a communication network may utilizethe same sequences for sector specific scrambling sequences.

Referring to FIG. 6, a multiple access wireless communication system 600according to another embodiment is illustrated. In the event when thesame sets of user specific and sector specific scrambling sequences areutilized in multiple cells, e.g. cells 602, 604, and 606, interferencecoming from the adjacent cells may lead to channel estimation accuracydegradation due to pilot symbol collision. For example, a channelestimate within the sector of interest may be biased by the channel of amobile station from the adjacent cell which mobile station has the sameuser specific and sector specific scrambling. To avoid such a bias, acell specific scrambling may be utilized, in addition to the userspecific scrambling and sector specific scrambling. A cell specificscrambling schema may be defined by Y_(c)=[Y_(1,c), . . . , Y_(N) _(P)_(s)]^(T) which is a vector of scalar functions that multiply therespective sequence of pilot symbols for every mobile station in thecell. The overall sequences of pilot symbols Z_((q,s,c))=[Z_(1,(q,s,c)),. . . , Z_(N) _(P) _(,(q,s,c))]^(T) which corresponds to a mobilestation with q-th user specific scrambling in the s-th sector of thec-th cell may defined as follows. If sector specific scrambling isutilized:Z _(k,(q,s,c)) =S _(k,q) ·X _(k,s) ·Y _(k,c), 1≦k≦N _(P), 1≦s≦S, c=1, 2,. . .    (10)If sector specific scrambling is not utilized:Z _(k,(q,s,c)) =S _(k,q) ·Y _(k,c), 1≦k≦N _(P), 1≦s≦S, c=1, 2, . . .  (11)

As already mentioned, the use of sector specific scrambling isrecommended when Q>1 and is not recommended when Q=1.

Unlike user specific and sector specific scrambling, no particularoptimization of cell specific scrambling sequences need be utilized. Thetwo design parameters that may be utilized are that:

-   -   All the elements of cell specific scrambling sequences have        equal modulus.    -   Cell specific scrambling sequences differ substantially for        different cells.

In the absence of pre-determined assignment of cell specific scramblingsequences over a network of base stations, a (pseudo)-random cellspecific scrambling sequences from some constant modulus (PSK)constellation such as QPSK, 8-PSK may be utilized in forming the Y cellspecific sequences. To further enhance randomization of cell specificscrambling and avoid bad steady combinations of scrambling sequences,cell specific scrambling may be changed periodically in a(pseudo-)random fashion. In some embodiments, the periodic change may beevery frame, superframe, or multiple frames or superframes.

FIG. 7 is a block diagram of an embodiment of a transmitter system 710and a receiver system 750 in a MIMO system 700. At transmitter system710, traffic data for a number of data streams is provided from a datasource 712 to a transmit (TX) data processor 714. In an embodiment, eachdata stream is transmitted over a respective transmit antenna. TX dataprocessor 714 formats, codes, and interleaves the traffic data for eachdata stream based on a particular coding scheme selected for that datastream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed on provided by controller 130.

The modulation symbols for all data streams are then provided to a TXprocessor 720, which may further process the modulation symbols (e.g.,for OFDM). TX processor 720 then provides N_(T) modulation symbolstreams to N_(T) transmitters (TMTR) 722 a through 722 t. Eachtransmitter 722 receives and processes a respective symbol stream toprovide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 722 a through 722 t are thentransmitted from N_(T) antennas 124 a through 124 t, respectively.

At receiver system 750, the transmitted modulated signals are receivedby N_(R) antennas 752 a through 752 r and the received signal from eachantenna 752 is provided to a respective receiver (RCVR) 754. Eachreceiver 754 conditions (e.g., filters, amplifies, and downconverts) arespective received signal, digitizes the conditioned signal to providesamples, and further processes the samples to provide a corresponding“received” symbol stream.

An RX data processor 760 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 754 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. Theprocessing by RX data processor 760 is described in further detailbelow. Each detected symbol stream includes symbols that are estimatesof the modulation symbols transmitted for the corresponding data stream.RX data processor 760 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 760 is complementary to thatperformed by TX processor 720 and TX data processor 714 at transmittersystem 710.

RX processor 760 may derive an estimate of the channel response betweenthe N_(T) transmit and N_(R) receive antennas, e.g., based on the pilotinformation multiplexed with the traffic data. RX processor 760 mayidentify the pilot symbols according to pilot patterns stored in memory,e.g. memory 772 that identify the frequency subcarrier and symbol periodassigned to each pilot symbol.

In addition, the user specific, sector specific, and cell specificscrambling sequences may be stored in memory so that they may beutilized by RX processor 760 to multiply the received symbols so thatthe proper decoding can occur.

The channel response estimate generated by RX processor 760 may be usedto perform space, space/time processing at the receiver, adjust powerlevels, change modulation rates or schemes, or other actions. RXprocessor 760 may further estimate the signal-to-noise-and-interferenceratios (SNRs) of the detected symbol streams, and possibly other channelcharacteristics, and provides these quantities to a controller 770. RXdata processor 760 or controller 770 may further derive an estimate ofthe “operating” SNR for the system. Controller 770 then provides channelstate information (CSI), which may comprise various types of informationregarding the communication link and/or the received data stream. Forexample, the CSI may comprise only the operating SNR. The CSI is thenprocessed by a TX data processor 778, which also receives traffic datafor a number of data streams from a data source 776, modulated by amodulator 780, conditioned by transmitters 754 a through 754 r, andtransmitted back to transmitter system 710.

At transmitter system 710, the modulated signals from receiver system750 are received by antennas 724, conditioned by receivers 722,demodulated by a demodulator 740, and processed by a RX data processor742 to recover the CSI reported by the receiver system. The reported CSIis then provided to controller 730 and used to (1) determine the datarates and coding and modulation schemes to be used for the data streamsand (2) generate various controls for TX data processor 714 and TXprocessor 720.

Controllers 730 and 770 direct the operation at the transmitter andreceiver systems, respectively. Memories 732 and 772 provide storage forprogram codes and data used by controllers 730 and 770, respectively.The memories 732 and 772 store the pilot patterns in terms of clusterlocations, user specific scrambling sequences, sector specificscrambling sequences, if utilized, and cell specific scramblingsequences, if utilized. In some embodiments, multiple pilot patterns arestored in each memory so that the transmitter may transmit and thereceiver may receive both frequency selective pilot patterns and timeselective pilot patterns. Also, combination pilot patterns havingclusters geared for time selective channels and frequency selectivechannels may be utilized. This allows a transmitter to transmit aspecific pattern based upon a parameter, such a random sequence, or inresponse to an instruction from the base station.

Processors 730 and 770 then can select which of the pilot patterns, userspecific scrambling sequences, sector specific scrambling sequences, andcell specific scrambling sequences are to be utilized in transmission ofthe pilot symbols.

At the receiver, various processing techniques may be used to processthe N_(R) received signals to detect the N_(T) transmitted symbolstreams. These receiver processing techniques may be grouped into twoprimary categories (i) spatial and space-time receiver processingtechniques (which are also referred to as equalization techniques); and(ii) “successive nulling/equalization and interference cancellation”receiver processing technique (which is also referred to as “successiveinterference cancellation” or “successive cancellation” receiverprocessing technique).

While FIG. 7 illustrates a MIMO system, the same system may be appliedto a multi-input single-output system where multiple transmit antennas,e.g. those on a base station, transmit one or more symbol streams to asingle antenna device, e.g. a mobile station. Also, a single output tosingle input antenna system may be utilized in the same manner asdescribed with respect to FIG. 7.

Referring to FIG. 8, a flow chart of a method of pilot symbol generationaccording to an embodiment is illustrated. A plurality of pilot symbolclusters is selected to be transmitted during a hop region from aparticular mobile station, block 800. These pilot symbol clusters may beall aligned for transmission in a frequency selective (FIG. 3A), a timeselective channel (FIG. 3B), or a combination of clusters some of whichare aligned for transmission in a frequency selective and a timeselective channel.

Once the pilot symbol clusters are selected, a determination is made asto whether the cluster of the base station in which the mobile stationis communicating supports, or is in communication with, multiple mobilestations, block 802. This determination may be based upon predeterminedknowledge of the network in which the mobile station. Alternatively,this information may be transmitted from the sector for the base stationas part of its pilot information or broadcast messages.

If the cluster does not support communication, or is not currently incommunication with multiple mobile stations, then scalar functions areapplied to the pilot symbols that are unique to the cluster with whichthe mobile station is communicating, block 804. In an embodiment, thescalar functions for each sector may be stored in the mobile station andutilized depending on a sector identification signal that is part of itspart of its pilot information or broadcast messages.

If the cluster does support communication with multiple mobile stations,then scalar functions are applied to the pilot symbols that are uniqueto the mobile station, block 806. In some embodiments, the scalarfunctions for each mobile station may be based upon its uniqueidentifier used for registration or provided to the device at the timeof manufacture.

After scalar functions, that are unique either to the sector with whichthe mobile station is communicating or the mobile station itself, areapplied to the pilot symbols, another sequence of scalar functions isapplied to the pilot symbols, block 808. The sequence of scalarfunctions relates to the cell in which the mobile station iscommunicating. This scalar function may vary over time, if each cell isnot specifically assigned scalar functions that are known by or providedto the mobile stations. After this operation, the pilot symbols may betransmitted from the mobile station to base station.

The scalar functions discussed with respect to FIG. 8, may in anembodiment involve a phase shift of each of the samples that constitutethe pilot symbols. As discussed with respect to FIGS. 4A, 4B, 5, and 6the scalar functions are selected so that each cluster of pilot symbolsis orthogonal to each other set of pilot symbols from the same mobilestation in other pilot symbol clusters and in the same and other pilotsymbol clusters for other mobile stations the same sector of the basestation.

In addition, the blocks described with respect to FIG. 8 may each beimplemented as one or more instructions on a computer readable media,such as a memory, which are implemented by a processor, controller, orother electronic circuitry.

Referring to FIG. 9, a flow chart of a method of altering pilot symbolpatterns according to an embodiment is illustrated. Informationregarding channel conditions is obtained, block 900. The information maycomprise SNR ratios at one or more sectors of the base stations, aselectivity of the channel at the base station, the desired traffictype, pedestrian or vehicular to which the base station is to beoptimized, delay spreads, or other characteristics of the channel.Further, the information may relate to periods of time, may be part of aregular maintenance operation on the base station or network of basestations, may be based on increased loading of the base station ornetwork of base stations, or other times.

The information is analyzed to determine the channel conditions of thesector or base station, block 902. The analysis may be a determinationwhether the channel is frequency selective, time selective, or acombination of both. The analysis is then utilized to determine a pilotsymbol pattern that is to be transmitted from mobile stations that maycommunicate with the sector or base station, block 904. These pilotsymbol clusters may be all aligned for transmission in a frequencyselective (FIG. 3A), a time selective channel (FIG. 3B), or acombination of clusters some of which are aligned for transmission in afrequency selective and a time selective channel. The specific pilotpattern selected may then be used by all of the mobile stations thatcommunicate with the base station or sector until such time as thediagnostic is performed again for the base station or sector.

To implement a specific pilot pattern at mobile stations communicatingat a base station or base station sector, an instruction may be sentfrom the base station or sector to the mobile stations as part of theinitialization or set-up procedure. In some embodiments, information aswhich pilot pattern, user specific scrambling sequence, sector specificscrambling sequence, and/or cell specific scrambling sequence is to beutilized may transmitted in a preamble of one or more data packets thatare transmitted from a base station to a mobile station at regularintervals or during initialization or set-up.

It should be noted that the analysis may also be utilized to determinethe number of pilot symbols to be transmitted in each cluster of pilotsymbols and the groupings of pilot symbols. Also, the blocks describedwith respect to FIG. 9 may each be implemented as one or moreinstructions on a computer readable media, such as a memory or removablemedia, which are implemented by a processor, controller, or otherelectronic circuitry.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing unitswithin a base station or a mobile station may be implemented within oneor more application specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,other electronic units designed to perform the functions describedherein, or a combination thereof.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin memory units and executed by processors. The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans as is known in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments may be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A wireless communication apparatus, comprising:at least one antenna; a memory that stores: at least one time selectivepilot pattern comprising first and second clusters of time selectivepilot symbols, said at least one time selective pilot patterncorresponding to a plurality of pilot symbols located in pilot symbolclusters each of which comprises a plurality of contiguous pilot symbolsspanning multiple frequency tones and one symbol period, wherein thefirst and second clusters of time selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of time selective pilot symbols isassigned to a maximum or minimum frequency of a hop region and none ofthe pilot symbols in the first and second clusters of time selectivepilot symbols are assigned to a first or last symbol period of the hopregion, and at least one frequency selective pilot pattern comprisingfirst and second clusters of frequency selective pilot symbols, said atleast one frequency selective pilot pattern corressponding to anotherplurality of pilot symbols located in pilot symbol clusters each ofwhich comprises a plurality of contiguous pilot symbols spanningmultiple symbol periods and one frequency subcarrier, wherein the firstand second clusters of frequency selective pilot symbols have orthogonalpilot symbols , and wherein only one pilot symbol in each of the firstand second clusters of frequency selective pilot symbols is assigned tothe first or last symbol period of the hop region and none of the pilotsymbols in the first and second clusters of frequency selective pilotsymbols are assigned to the maximum or minimum frequency of the hopregion; and a processor coupled with the at least one antenna and thememory, the processor configured to select one pilot pattern of the atleast one time selective pilot pattern or the at least one frequencyselective pilot pattern, wherein the processor is configured to placethe pilot symbols of the selected pilot pattern close to the edges ofthe hop region according to a first order approximation of acommunications channel.
 2. The wireless communication apparatus of claim1, wherein the at least one time selective pilot pattern comprises aplurality of time selective pilot patterns, the at least one frequencyselective pilot pattern comprises a plurality of frequency selectivepilot patterns, and wherein the processor is configured to select atleast one of the plurality of time selective pilot patterns or at leastone of the plurality of frequency selective pilot patterns.
 3. Thewireless communication apparatus of claim 1, wherein the processor isadapted to select a time selective pilot pattern or a frequencyselective pilot pattern based upon a parameter.
 4. The wirelesscommunication apparatus of claim 3, wherein the parameter comprises apredetermined threshold.
 5. The wireless communication apparatus ofclaim 3, wherein the parameter is dynamically updated in response to asignal received at the wireless communication apparatus.
 6. The wirelesscommunication apparatus of claim 3, wherein the parameter comprises apre-determined optimization of the network in which the wirelesscommunication apparatus is to operate.
 7. The wireless communicationapparatus of claim 1, wherein the memory further stores a plurality ofsequences that are orthogonal to each other sequence of the plurality ofsequences and wherein the processor is configured to selectivelyinstruct multiplication of the pilot symbols of the pilot pattern withsome of the sequences of the plurality of sequences prior totransmission of the pilot pattern.
 8. The wireless communicationapparatus of claim 7, wherein the memory further stores anotherplurality of sequences and wherein the processor is configured toselectively instruct multiplication of the pilot symbols of the pilotpattern with both some of the sequences of the plurality of sequencesand some of the another plurality of sequences prior to transmission ofthe pilot pattern.
 9. The wireless communication apparatus of claim 1,wherein the memory is adapted to store a frequency selective pilotpattern having quasi-orthogonal pilot symbols.
 10. The wirelesscommunication apparatus of claim 1, wherein the memory is adapted tostore a time selective pilot pattern having quasi-orthogonal pilotsymbols.
 11. A method of pilot symbol transmission in a wirelesscommunication system, comprising: obtaining information regardingchannel conditions of a channel from at least one sector of a basestation; determining a selectivity of the channel based upon theinformation; choosing a pattern of pilot symbols based upon theselectivity of the channel, wherein the pattern of pilot symbols isselected from at least one time selective pilot pattern comprising firstand second clusters of time selective pilot symbols, said at least onetime selective pilot pattern corresponding to a plurality of pilotsymbols located in pilot symbol clusters each of which comprises aplurality of contiguous pilot symbols spanning multiple frequency tonesand one symbol period, wherein the first and second clusters of timeselective pilot symbols have orthogonal pilot symbols, and wherein onlyone pilot symbol in each of the first and second clusters of timeselective pilot symbols is assigned to a maximum or minimum frequency ofa hop region and none of the pilot symbols in the first and secondclusters of time selective pilot symbols are assigned to a first or lastsymbol period of the hop region, and at least one frequency selectivepilot pattern comprising first and second clusters of frequencyselective pilot symbols, said at least one frequency selective pilotpattern corresponding to another plurality of pilot symbols located inpilot symbol clusters each of which comprises a plurality of contiguouspilot symbols spanning multiple symbol periods and one frequencysubcarrier, wherein the first and second clusters of frequency selectivepilot symbols have orthogonal pilot symbols, and wherein only one pilotsymbol in each of the first and second clusters of frequency selectivepilot symbols is assigned to the first or last symbol period of the hopregion and none of the pilot symbols in the first and second clusters offrequency selective pilot symbols are assigned to the maximum or minimumfrequency of the hop region; and placing the pilot symbols of theselected pilot pattern close to the edges of the hop region according toa first order approximation of a communications channel.
 12. The methodof claim 11, wherein in the step of determining the selectivity of thechannel the channel is classified as frequency selective or timeselective.
 13. H The method of claim 11, wherein in the step ofdetermining the selectivity of the channel, a frequency selectivity anda time selectivity is determined.
 14. The method of claim 11, wherein inthe step of choosing the pattern of clustered pilot symbols theclustered pilot symbols are optimized for one or both frequencyselective and time selective conditions.
 15. The method of claim 11,further comprising transmitting information indicating the pattern ofclustered pilot symbols to a plurality of users so that the userstransmit pilot symbols according to the pattern to the sector of thebase station.
 16. A wireless communication apparatus capable oftransmitting a plurality of symbols each of which is transmittedutilizing a frequency subcarrier of a group of contiguous frequencysubcarriers that range from a minimum frequency to a maximum frequencyand during a symbol period of a group of contiguous symbol periods thatrange from a first symbol period to a last symbol period, the wirelesscommunication apparatus comprising: at least one antenna; a memory thatstores a plurality of time selective pilot patterns comprising first andsecond clusters of time selective pilot symbols each comprising aplurality of clusters each of which comprises a plurality of contiguouspilot symbols located in pilot symbol clusters each of which comprises aplurality of contiguous pilot symbols spanning multiple frequency tonesand one symbol period, wherein the first and second clusters of timeselective pilot symbols have orthogonal pilot symbols, and wherein onlyone pilot symbol in each of the first and second clusters of timeselective pilot symbols is assigned to a maximum or minimum frequency ofa hop region and none of the pilot symbols in the first and secondclusters of time selective pilot symbols are assigned to a first or lastsymbol period of the hop region, and at least one frequency selectivepilot pattern comprising first and second clusters of frequencyselective pilot symbols, the at least one frequency selective pilotpattern corresponding to another plurality of pilot symbols located inpilot symbol clusters each of which comprises a plurality of contiguouspilot symbols spanning multiple symbol periods and one frequencysubcarrier, wherein the first and second clusters of frequency selectivepilot symbols have orthogonal pilot symbols, and wherein only one pilotsymbol in each of the first and second clusters of frequency selectivepilot symbols is assigned to the first or last symbol period of the hopregion and none of the pilot symbols in the first and second clusters offrequency selective pilot symbols are assigned to the maximum or minimumfrequency of the hop region; and a processor coupled with the pluralityof antennas and the memory, the processor configured to cause one pilotpattern of the plurality of pilot patterns to be transmitted from the atleast one antenna during the group of contiguous symbol periodsutilizing the group of contiguous frequency subcarriers, wherein theprocessor is configured to place the pilot pattern close to the edges ofthe hop region according to a first order approximation of acommunications channel.
 17. The wireless communication apparatus ofclaim 16, wherein the plurality of pilot patterns comprise at least onetime selective pilot pattern and at least one frequency selective pilotpattern.
 18. The wireless communication apparatus of claim 16, whereinthe memory further stores a plurality of sequences that are orthogonalto each other sequence of the plurality of sequences and wherein theprocessor is configured to selectively instruct multiplication of thepilot symbols of the pilot pattern with some of the sequences of theplurality of sequences prior to decoding the pilot symbols.
 19. Thewireless communication apparatus of claim 16, wherein the memory furtherstores a plurality of sequences that are quasi-orthogonal to each othersequence of the plurality of sequences and wherein the processor isconfigured to selectively instruct multiplication of the pilot symbolsof the pilot pattern with some of the sequences of the plurality ofsequences prior to decoding the pilot symbols.
 20. The wirelesscommunication apparatus of claim 19, wherein the memory further storesanother plurality of sequences and wherein the processor is configuredto selectively instruct multiplication of the pilot symbols of the pilotpattern with both some of the sequences of the plurality of sequencesand some of the another plurality of sequences prior to decoding thepilot symbols.
 21. The wireless communication apparatus of claim 16,wherein the processor is configured to select selects the pilot patternto be transmitted based upon an instruction received at the at least oneantenna.
 22. The wireless communication apparatus of claim 16, whereinthe at least one antenna comprises a plurality of antennas and whereinthe processor is configured to cause multiple pilot patterns of theplurality of pilot patterns to be transmitted from the multiple antennasduring the group of contiguous symbol periods utilizing the group ofcontiguous frequency subcarriers.
 23. The wireless communicationapparatus of claim 22, wherein the memory further stores a plurality ofsequences that are orthogonal to each other sequence of the plurality ofsequences and wherein the processor is configured to selectivelyinstruct multiplication of the pilot symbols of each of the multiplepilot pattern with a different sequences of the plurality of sequencesprior to transmission of the multiple pilot patterns.
 24. The wirelesscommunication apparatus of claim 16, wherein the processor is configuredto utilize one pilot pattern of the plurality of pilot patterns todecode multiple pilot symbol groups transmitted by a plurality ofwireless devices and received at the at least one antenna.
 25. Anon-transitory computer readable medium encoded with computer executableinstructions for reading a data packet for transmission in a wirelessnetwork, the data packet including a preamble portion that identifies acluster pilot pattern having a plurality of time or frequency selectiveclusters to be transmitted by a receiver of the data packet including atleast one each of a frequency-selective pilot pattern or atime-selective pilot pattern, wherein the time selective patterncomprises first and second clusters of time selective pilot symbols andthe first and second clusters of time selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of time selective pilot symbols isassigned to a maximum or minimum frequency of a hop region and none ofthe pilot symbols in the first and second clusters of time selectivepilot symbols are assigned to a first or last symbol period of the hopregion, and wherein the frequency selective pilot pattern comprisesfirst and second clusters of frequency selective pilot symbols and thefirst and second clusters of frequency selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of frequency selective pilot symbols isassigned to the first or last symbol period of the hop region and noneof the pilot symbols in the first and second clusters of frequencyselective pilot symbols are assigned to the maximum or minimum frequencyof the hop region, and instructions for placing the symbols of thecluster pilot pattern close to the edges of the hop region according toa first order approximation of a communications channel.
 26. Thecomputer readable medium of claim 25, wherein the computer executableinstructions are adapted to read a packet having a preamble portion thatincludes information as to which sequence of a plurality of orthogonalsequences available at a receiver is to be utilized by the receiver ofthe data packet to multiply the samples that comprise pilot symbols ofthe pilot pattern prior to transmission of the pilot symbols by thereceiver of the data packet.
 27. A non-transitory computer readablemedium encoded with: computer executable instructions for pilot symboltransmission in a wireless communication system, the computer executableinstructions comprising: instructions for obtaining informationregarding channel conditions from at least a sector of a base station;instructions for determining, based upon the information, a selectivityof the channel; instructions for setting a pattern of pilot symbolshaving a plurality of time or frequency selective clusters based uponthe selectivity of the channel, wherein the time selective patterncomprises first and second clusters of time selective pilot symbols andthe first and second clusters of time selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of time selective pilot symbols isassigned to a maximum or minimum frequency of a hop region and none ofthe pilot symbols in the first and second clusters of time selectivepilot symbols are assigned to a first or last symbol period of the hopregion, and wherein the frequency selective pilot pattern comprisesfirst and second clusters of frequency selective pilot symbols and thefirst and second clusters of frequency selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of frequency selective pilot symbols isassigned to the first or last symbol period of the hop region and noneof the pilot symbols in the first and second clusters of frequencyselective pilot symbols are assigned to the maximum or minimum frequencyof the hop region; and instructions for placing the pattern of pilotsymbols close to the edges of the hop region according to a first orderapproximation of a communications channel.
 28. A processing systemcomprising: an input port; an output port; and processing circuitryconfigured to: obtain information from an input port regarding channelconditions from at least a sector of a base station; determine, basedupon the information, a selectivity of the channel; set a pattern ofclustered pilot symbols having a plurality of time or frequencyselective clusters based upon the selectivity of the channel and tooutput a selection of the set pattern of pilot symbols through theoutput port, wherein the time selective pattern comprises first andsecond clusters of time selective pilot symbols and the first and secondclusters of time selective pilot symbols have orthogonal pilot symbol ,and wherein only one pilot symbol in each of the first and secondclusters of time selective pilot symbols is assigned to a maximum orminimum frequency of a hop region and none of the pilot symbols in thefirst and second clusters of time selective pilot symbols are assignedto a first or last symbol period of the hop region, and wherein thefrequency selective pilot pattern comprises first and second clusters offrequency selective pilot symbols and the first and second clusters offrequency selective pilot symbols have orthogonal pilot symbols, andwherein only one pilot symbol in each of the first and second clustersof frequency selective pilot symbols is assigned to the first or lastsymbol period of the hop region and none of the pilot symbols in thefirst and second clusters of frequency selective pilot symbols areassigned to the maximum or minimum frequency of the hop region; andplace the pilot pattern of pilot symbols close to the edges of the hopregion according to a first order approximation of a communicationschannel.
 29. A non-transitory computer-readable medium encoded withinstructions for processing a communication signal, the instructionscomprising code for: obtaining information regarding channel conditionsfrom at least a sector of a base station; determining, based upon theinformation, a selectivity of the channel; setting a pattern of pilotsymbols having a plurality of time or frequency selective clusters basedupon the selectivity of the channel, wherein the time selective patterncomprises first and second clusters of time selective pilot symbols andthe first and second clusters of time selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of time selective pilot symbols isassigned to a maximum or minimum frequency of a hop region and none ofthe pilot symbols in the first and second clusters of time selectivepilot symbols are assigned to a first or last symbol period of the hopregion, and wherein the frequency selective pilot pattern comprisesfirst and second clusters of frequency selective pilot symbols and thefirst and second clusters of frequency selective pilot symbols haveorthogonal pilot symbols, and wherein only one pilot symbol in each ofthe first and second clusters of frequency selective pilot symbols isassigned to the first or last symbol period of the hop region and noneof the pilot symbols in the first and second clusters of frequencyselective pilot symbols are assigned to the maximum or minimum frequencyof the hop region; and placing the pattern of pilot symbols close to theedges of the hop region according to a first order approximation of acommunications channel.